1. Field of the Invention
The invention relates to textile tow cutting processes and apparatus. More particularly, the invention relates to tow cutting processes and apparatus which perform the cutting by transverse or orthogonal movement of a cutting surface with respect to the direction of wrapping of textile tow on a textile tow support.
2. Description of the Prior Art
Several processes are currently used for continuously cutting textile tow into staple of primarily uniform lengths or into a specific distribution of staple lengths. These processes are unsatisfactory either because of the short life of the cutting surfaces or the nonuniform staple lengths produced thereby.
A well known process for cutting tow, known as the "Gru-Gru System", is described in German Pat. No. 665,939. In this machine the tow is held between two rubber coated slotted wheels while knives affixed on a knife head pass through the slots so that the two is cut into staple in the slots by the shearing effect of the knives.
In another process, tow is introduced through the axis of a rotating wheel and is transported radially outward from the axis of the wheel through a tube into the path of a cutting knife affixed to the wheel at its outer circumference. The cutting of tow is produced by shearing between the cutting knife carried by the rotating wheel and a stationary knife affixed outside the circumference of the wheel in close proximity to the path of the rotating cutting knife. Cutting of the staple produces crushing of the fiber portions of the tow.
Another process cuts tow into staple by transporting tow to a cutting zone where cutting is produced by a rotating disk knife. The tow is carried into one of the slots of a slotted guide disk by means of an aspirator and transported by the disk to the rotating disk knife where the tow is cut into staple and removed by a second aspirator. During cutting, the tow is not held on both sides of the rotating disk knife so that it is partially pushed sideways during cutting which causes nonuniform staple lengths.
Another type of tow cutting machine is described in U.S. Pat. Nos. 3,485,120 and 3,503,100. In this machine, tow cutting into staple is performed by a wheel which consists of a plurality of radially outward pointing stationary knives which are fixedly connected to a pair of disks. The tow cut by the force exerted on the tow by a pressure roll which rides against the outermost layer of tow which is wound over the surface of the knives. After the layers of tow attain a certain thickness, the pressure roll presses with sufficient force against the outside layer of the tow to cause the knife edges to shear the innermost layer of tow at its points of contact with the knives. The cut staple is forced radially inward from surface contact with the knives to a collection point located at the center of the disks from which it is transported away. Continuously, new layers of the tow originating from the outside come in contact with the knives and are cut. This machine differs substantially from the present invention in that cutting of the tow is accomplished by static pressure between the cutting surface of the knives and the tow. Unlike the dynamic cutting of the present invention, the resultant stationary cutting is accomplished by high frictional forces which enhance dulling of the knives and fusing of the staple ends.
U.S. Pat. No. 3,768,355 discloses a tow cutting apparatus in which cutting is performed by stationary knives which are radially or axially disposed with respect to a cylindrical mounting frame. The tow is fed radially against or axially against the respective stationary radially or axially disposed cutting surfaces of the knives. The apparatus disclosed in U.S. Pat. No. 3,768,355 differs from the present invention in that it cuts tow by static pressure between the cutting surface of the knives and the tow.
Those machines using stationary cutting knives have the disadvantage of crushing the tow filaments during cutting which causes a concomitant rapid dulling of cutting surfaces of the knives because of the action of high frictional forces. Cutting of tow with dull knives produces unacceptable staple because of gluing together of the cut fiber ends as a result of the heating of the fibers during cutting by the high frictional forces and also results in staple of multiple lengths when some of the cutting knives are not sharp enough to completely sever the tow. Multiple length staple when processed results in unacceptable yarn products. The presence of multiple length staple is presently eliminated by replacement of the knives after short periods of time. It has been found that replacement of the knives in the prior art apparatus is required after two to four hours of operation with remounting times from twenty minutes to one hour being necessary.
Those prior art machines having moving cutting knives produce a draw cut of the tow between the rapidly rotating cutting knives and the tow. Because of the fact that the tow is not supported on both sides of the cutting knives during cutting, portions of the tow are pulled axially with respect to the axis of the tow which results in uneven staple lengths.
Other machines were developed wherein one or more rotary knife plates are moved vertically through the tow filaments to execute a draw cut between the rapidly moving knives and the tow. In one of these machines, rotating knife disks arranged in the shape of a star cut the tow into staple. In this machine the tow is suspended between two link changes having rubber coated surfaces. The rotating knives cut the tow through the spaces in the link chains. The knives in this machine do not have the disadvantage of a short cutting life found in the other well known apparatus for cutting tow. However, its complex construction has militated against its widespread use.